Several prior art cell culturing bioreactors have been disclosed. Examples are found in U.S. Pat. Nos. 4,647,539, 4,603,109, 4,391,912, 4,317,886, 4,242,460, 4,242,459, 4,228,243, and 4,220,725. While these prior art bioreactors permit the culturing of cells, they represent a combination of compromise cell culturing conditions owing to their configuration and material composition. Particularly, the geometric configuration of the cell culturing chamber leads to the circumstance where cells exist in regions where insufficient nutrients are present. This circumstance is predicated on the fact that the rate of consumption of the growth limiting nutrient required for culturing the cells exceeded the rate of diffusion through the cell matrix of the growth limiting nutrient. As a result, the growth limiting nutrient in some cases does not reach certain areas of the cell culturing chamber.
Other drawbacks relating to the prior art bioreactors relate to their construction materials. Particularly, the prior art bioreactors are conventionally constructed of silicone, glass, rubber, and polypropylene or other polymer. As such, each of these elements of separate materials must be adhesively bonded together. Owing to the fact that the materials are chemically dissimilar, the adhesive bonding is limited only to a mechanical type bond between the distinct bioreactor elements. As a result, repeated sterilization of the bioreactors leads to the degradation of their structural integrity and consequent failure. Failure, of course, being an undesirable characteristic in a relatively expensive piece of laboratory equipment.
The prior art attempts to solve the geometric isolation of certain cells within a culturing chamber have involved the creation of dual hollow fiber bioreactors. This construction involves placing a hollow fiber tube concentrically within another length of hollow fiber and immobilizing the cells in the annular gap existing between the concentrically related fibers. The limiting aspect of this configuration has been that either of one of the fibers has been made permeable to fluid nutrient constituents and the other fiber being permeable to gas nutrient constituents rather than a combination thereof.
The prior art has been unable to successfully create a dual hollow fiber reactor wherein both the inner and outer tubes are comprised of the same materials and therefore have the same permeability to the most desirable nutrient constituents. A typical construction of such a prior art bioreactor has included a polypropylene outer hollow fiber with a silicone tubule inserted concentrically therein or the reverse, that is, a silicone outer fiber with a polypropylene inner fiber. The remaining elements of the bioreactor comprising rubber plugs and a glass outer shell.
Although thee prior art solution discussed above more nearly attempted to create the ideal geometric cell culturing chamber in terms of distance from the nutrient source, i.e., the membrane, the construction materials of the prior art bioreactors limited the usefulness of the reactors to replicate cell growth conditions in animals and/or humans. Extensive research has determined that in the human body cells rarely exist beyond a distance of 100 microns from a nutrient capillary. As such, researchers have attempted to replicate this configuration with man-made materials. However, the stumbling block has been not only achieving the cell/nutrient source distance separation but also achieving satisfactory nutrient supplies from all sides of the cell. That is, the prior bioreactors have only been able to supply gaseous nutrients from one side and fluidized nutrients from the other. The situation of having fluidized nutrients from both sides has not been successfully achieved.
Additionally, the prior art bioreactors have consistently produced large populations of dead cells in their culturing chambers. This phenomena exists because the cells closest to the nutrient membrane push cells which are spaced away from the membrane further away from the membrane. Once the separation exceeds the diffusive capacity of the nutrients, the cell dies. Once a cell dies, it becomes more easily compressible because it can no longer exert growth pressure of its own against surrounding cells. As a result, growing cells located closer to the nutrient source are able to continually push those cells which are spaced more remotely further into their respective remote area. Eventually, the growing cells generate a band of dead cells which is continually crushed by the growing pressure of the living cells. Since the dead cells compact more easily into solids than do the living cells, the population of compacted dead cells can equal or exceed the population of living cells.
Hence, the prior art bioreactors although useful for culturing cells also include severe limitations to their utility because of both their ability to create two cell populations within their culturing chambers and also, owing to their distinct component part construction, limited reusability thereof. The present invention seeks to avoid the problems associated with prior art bioreactors through the combination of dual hollow fiber configuration and homopolymer material construction.